Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session Q01: Suspensions: Rheology 
Hide Abstracts 
Chair: Rishabh More, Purdue University Room: North 120 AB 
Tuesday, November 23, 2021 8:00AM  8:13AM 
Q01.00001: Shear thinning rheology in a concentrated suspension of fibers: the role of attractive interactions Md Monsurul Islam Khan, Rishabh V More, Arezoo M Ardekani Fiberreinforced composites are ubiquitously encountered in the engineering, automobile, and aerospace industries. Fabrication of these composites requires the mixing of fibers dispersed in a liquid, and the final structure is affected by fiber properties, interactions, and flow fields. A good understanding of the rheology of fiber suspensions can aid in the design and optimization of the fabrication processes. To this end, we simulate the simple shear flow of fiber suspensions by accounting for shortrange lubrication, van der Waals attractive, electrostatic repulsion interactions, as well as friction between fibers. Direct numerical simulations are performed using the Immersed Boundary Method where the fibers are modeled as flexible slender bodies governed by the EulerBernoulli beam theory and the fluid flow is resolved using the NavierStokes equations. The simulation results for the suspension viscosity and yield stress are consistent with the experimental data from the literature for polyamide fiber suspensions. The shearthinning behavior becomes stronger as we increase the magnitude of attractive interactions. Furthermore, we perform a parametric study varying fiber flexibility, volume fraction, aspect ratio, inertia and examine suspension viscosity and yield stress. 
Tuesday, November 23, 2021 8:13AM  8:26AM 
Q01.00002: Unifying disparate ratedependent regimes in nonBrownian suspensions Rishabh V More, Arezoo M Ardekani A nonBrownian suspension undergoes shear thinning (decreasing viscosity) at low shear rates followed by a Newtonian plateau (constant viscosity) at intermediate shear rates which transitions to shear thickening (increasing viscosity) beyond a critical shear rate/stress and finally, a second shearthinning transition is observed at extremely high shear rates. We quantitatively unify all the disparate nonNewtonian regimes and the corresponding transitions with increasing shear rates. Direct comparison with experimental data from the literature corroborates the validity of the model. Inclusion of traditional hydrodynamic, DLVO, and contact forces with constant friction reproduce the initial thinning and the shear thickening transition. However, to quantitatively capture the intermediate Newtonian plateau and the second shear thinning, an additional nonhydrodynamic interaction of nonDLVO origin and a decreasing coefficient of friction, respectively, are essential; thus, providing the first explanation for the Newtonian plateau along with reproducing the second shear thinning in a single framework. We demonstrate the model versatility in predicting a variety of other ratedependent behaviors, normal stress differences, and particle tribology effects on suspension rheology. 
Tuesday, November 23, 2021 8:26AM  8:39AM 
Q01.00003: Experimental study of magnetorheological fluids formed used particle mixtures Vignesh Sridhar, Islam Benouaguef, Ian S Fischer, Pushpendra Singh

Tuesday, November 23, 2021 8:39AM  8:52AM Not Participating 
Q01.00004: Dynamics and rheology of periodically driven suspensions Zhouyang Ge, Gwynn J Elfring Suspensions of hydrodynamically interacting particles are important model systems for a range of natural and industrial problems, such as protein transport in tissues or rational design of novel metamaterials, thus understanding their dynamics and rheology is of key importance. Most natural and industrial flows are timedependent; so, it is particularly relevant to examine the suspension behaviour when it is driven periodically. Recent work in the literature have identified two mechanisms for noncolloidal suspensions of spherical particles to undergo reversibleirreversible transitions in oscillatory shear, due to either interparticle collision or attraction. However, none of the studies has included longrange hydrodynamic interactions, which may be crucial to the transient dynamics of the system. Here, we numerically examine the suspension dynamics and rheology with full hydrodynamic interactions using a newly developed fast Stokesian dynamics method. The effect of particle geometry, modelled from rigidly connecting spherical beads into composites, will also be discussed. 
Tuesday, November 23, 2021 8:52AM  9:05AM 
Q01.00005: Effects of volume fraction and particle shape on the rheological properties of oblate spheroid suspensions Junwei Guo, Qi Zhou, Ron Wong Coupled lattice Boltzmann and discrete element methods were employed to investigate the rheological properties of oblate spheroid suspensions in a Newtonian fluid. The volume fraction of the particles is varied, along with the particle aspect ratio. As the particle shape is varied from sphere to oblate, we observe an increase of the relative viscosity, as well as an increase of the particle contacts and the contact distance. We also report the first and second normal stress difference coefficients as they vary with the volume fraction and/or the particle shape. The more oblate particles in denser suspensions are observed to reorient systematically subject to the shear flow. We recast the viscosity data using the KriegerDougherty formula and report the modified Einstein coefficients. 
Tuesday, November 23, 2021 9:05AM  9:18AM 
Q01.00006: Rheology of dense, bidispersed suspensions: Segregative phenomenon induced by a flow perturbation Alessandro Monti, Marco E Rosti We have studied the phenomenon of segregation of a nonBrownian dense suspension (volume fraction φ = 0.5) of rigid, inertialess, neutrally buoyant, bidispersed particles, with a large particlesizeratio a2/a1 = 3, being a1 and a2 the radii of the smaller and larger particles in the suspension, respectively. The particles have been immersed in a plain shearflow of a Newtonianfluid at a low Reynolds number. The shearrate was varied to analyse the whole rheological behaviour of the suspension. To induce the segregation of the larger particles from the smaller ones, we perturbed the underline shear flow by adding a simple sinusoidal wave to the streamwise velocity, with the wavyvariations in the direction of the shear. We carried out a parametric study varying the amplitude and the wavenumber of the sinusoidal disturbance to analyse their relative importance in the onset of the phenomenon of segregation. The study has been performed by means of numerical simulations that tackle the NewtonEuler equations governing the dynamics of the particles. Preliminary results show that the larger particles tend to migrate towards the regions of minimum shear if the amplitude of the perturbation is above a threshold limit. An increasing wavenumber can help to segregate the particles. 
Tuesday, November 23, 2021 9:18AM  9:31AM 
Q01.00007: Experimental evidence of viscousinertial transition in noncolloidal granular suspensions Franco A Tapia, Elisabeth L Guazzelli, Olivier Pouliquen, Mie Ichihara Dense granular suspensions can exhibit different regimes depending on the boundary conditions and stress distribution. In general, the flow is mainly controlled by the ratio of the shear rate and the particle pressure, which could be partially well described by a frictional approach for a dilatant granular media. However, as the shear rate increases and the fluid viscosity decreases, the flow can transit from a viscous to an inertial regime. In absence of constitutive equations, dimensional analysis does not give the crucial information to determine this transition, and except for some numerical works, there is not substantial experimental evidence of this phenomenon. 
Tuesday, November 23, 2021 9:31AM  9:44AM 
Q01.00008: Rheology of mobile sediment beds sheared by viscous, pressuredriven flows Bernhard Vowinckel, Edward Biegert, Eckart H Meiburg, Pascale Aussillous, Élisabeth Guazzelli

Tuesday, November 23, 2021 9:44AM  9:57AM 
Q01.00009: Physical aging in aqueous nematic gels of a swelling nanoclay: Sol (phase) to gel (state) transition Mohammad Shoaib, Erin R Bobicki Aqueous suspensions of geometrically anisometric, nanosized sodiummontmorillonite (NaMt) display a sol–gel transition at very low solids concentrations. The microstructure of the gel formed at very low ionic strengths is considered electrostatically repulsive with a nematic character, and the gel state at ionic strengths where Debye length is of the order of particle size is conjectured to be free of physical aging. We investigated the nature of osmotically prepared NaMt suspensions at low ionic strength (~105 M), below and above the gel point. The sol phase exhibited very low yield stress than the gel state, without any sign of physical aging, thus behaving as an equilibrium state. In contrast, the gel exhibited signatures of physical aging, that is, an evolving microstructure that consolidated with time when left undisturbed thus behaving as out of equilibrium state. The physical aging behaviour became more pronounced at NaMt concentrations far above the gel point. A critical shear rate existed, below which no stable flows were possible in the gel state representing the microstructural reorganization timescale. Overall, NaMt suspensions in the gel state behave like systems that were out of equilibrium with an everevolving microstructure, in opposition to the assumption that low ionic strength NaMt gels are in an equilibrium phase. The possible origin of physical aging, such as the reversible orientation of Brownian anisotropic particles, stiffening of an existing microstructure, or reorganization of microstructure towards minimal energy configuration is discussed in detail. 
Tuesday, November 23, 2021 9:57AM  10:10AM 
Q01.00010: Singleparticle stress for a graphene particle Lorenzo Botto, Catherine Kamal, Adyant Agrawal, Simon Gravelle We studied the dynamics of graphene freelysuspended in simple shear flow, using a combination of molecular dynamics simulations and boundary integral simulations. Graphene is a platelike colloidal particle, whose nanoscopic thickness is comparable to that of a typical liquid solvent molecule. Unusual for platelike particles (e.g. clays) the thickness is also smaller than the hydrodynamic slip length characterising the relatively velocity at the fluidsolid boundary. This talk will examine the consequence of this geometric regime on the dynamics of graphene particles in shear flow, and on the ensuing rheology. For slip lengths larger than the particle thickness, the rotational dynamics predicted by Jeffery's theory ceases to occur. We recently demonstrate this behaviour by simulating 2D rigid particles that rotate only in the flowgradient plane as well as 3D particles that have fully 3dimensional orbits. This effect is also seen for mildly flexible particles and for particle concentrations beyond the classical dilute regime. Our simulations also indicate a substantial drop in suspension viscosity in this slip regime.In the talk, the physical origin of the drop in viscosity will be discussed in the dilute limit for the rigid case, based on the analysis of the singleparticle stresslet (moment of hydrodynamic traction) and a further integral term involving the integral of the slip velocity over the particle surface; this last term is usually ignored, as it is zero for nonslip particles, . The results show a nontrivial dependence of both these terms on the ratio of slip length and particle thickness, and on the geometric aspect ratio. We discuss whether negative contributions of the particle to the suspension viscosity are physically possible. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2023 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700